Light-emitting elements such as light-emitting diodes (LEDs) emit light when electrons combine with holes. Light-emitting elements consume low power, have a long life, can be installed in a limited space, and are resistant to vibrations.
A light-emitting element may include a light-emitting structure in which a GaN pattern of an n type, a light-emitting pattern, and a GaN pattern of a p type are stacked. Light is generated in the light-emitting pattern when carriers (e.g., electrons) of the GaN pattern of the n type combine with carriers (e.g., holes) of the GaN pattern of the p type.
A major challenge in the development of light-emitting elements is to improve light extraction efficiency. Light extraction efficiency denotes the proportion of light, which comes out of a light-emitting structure (into, for example, air or transparent resin that surrounds the light-emitting structure), in light generated within the light-emitting element. A light-emitting structure may have an optical refractive index of approximately 2.2 to 3.8, air may have an optical refractive index of 1, and transparent resin may have an optical refractive index of approximately 1.5.
For example, when a light-emitting structure has an optical refractive index of 3.4, a portion of light generated within the light-emitting structure may come out of the light-emitting structure into air at a critical angle of approximately 17 degrees and into transparent resin at a critical angle of approximately 26 degrees.
In this case, the light extraction efficiency of the light-emitting structure is approximately 2.2% when a portion of light generated within the light-emitting structure comes out of the light-emitting structure into air, and the light extraction efficiency of the light-emitting structure is approximately 4% when the portion of the light generated within the light-emitting structure comes out of the light-emitting structure into transparent resin. The other portion of the light is reflected by the surface of the light-emitting structure and trapped in the light-emitting structure.
A light-emitting structure may be made of a material containing InxAlyGa(1-x-y)N (0≦x≦1, 0≦y≦1). In order to develop a light-emitting element using InxAlyGa(1-x-y)N, it is important to form InxAlyGa(1-x-y)N having a low defect density. For example, InxAlyGa(1-x-y)N may be grown on a sapphire substrate. However, when the sapphire substrate is defective, InxAlyGa(1-x-y)N grown from the sapphire substrate may also be defective.
In addition, the entire region of a light-emitting pattern may not always be used equally. That is, only part of the light-emitting pattern may be used depending on the design of a light-emitting element. Thus, electric current may flow only in a specific region of the light-emitting pattern, and light may be emitted only from the specific region in which electric current flows. Consequently, the amount of light emitted may be reduced.